Semiconductor device and a method of manufacturing the same

ABSTRACT

A technique which improves the reliability in coupling between a bump electrode of a semiconductor chip and wiring of a mounting substrate, more particularly a technique which guarantees the flatness of a bump electrode even when wiring lies in a top wiring layer under the bump electrode, thereby improving the reliability in coupling between the bump electrode and the wiring formed on a glass substrate. Wiring, comprised of a power line or signal line, and a dummy pattern are formed in a top wiring layer beneath a non-overlap region of a bump electrode. The dummy pattern is located to fill the space between wirings to reduce irregularities caused by the wirings and space in the top wiring layer. A surface protection film formed to cover the top wiring layer is flattened by CMP.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2007-292079 filed onNov. 9, 2007 including the specification, drawings and abstract isincorporated herein by reference into its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method ofmanufacturing the same and more particularly to a technique useful for asemiconductor device used in an LCD (Liquid Crystal Display) driver.

Japanese Unexamined Patent Publication No. 2007-103848 discloses atechnique of reducing the semiconductor chip size. According to thistechnique, a pad and wirings are formed over an insulation film. Asurface protection film is formed over the insulation film including thepad and wirings and an opening is made in the surface protection film.The opening is formed over the pad to expose the pad surface. A bumpelectrode is formed over the surface protection film including thisopening. The pad is much smaller than the bump electrode. Consequentlywirings can be disposed beneath the bump electrode, in the same layer asthe pad. In other words, in this technique, wirings are disposed inspace made available under the bump electrode by reducing the pad size.

SUMMARY OF THE INVENTION

In recent years, LCDs which use liquid crystal display elements havebeen rapidly spreading. An LCD is controlled by a driver which drivesthe LCD. The LCD driver is comprised of a semiconductor chip which is,for example, mounted on a glass substrate. The semiconductor chip of theLCD driver has a plurality of transistors and multilayer wiring layerover its semiconductor substrate with bump electrodes over the surface.A bump electrode formed over the surface is coupled with the glasssubstrate through an anisotropic conductive film. The semiconductor chipand the glass substrate are thus coupled through the bump electrode. Forthe purpose of increasing the adhesive strength, it has been a commonpractice to increase the bump electrode area to make the area ofadhesion between the semiconductor chip and the glass substrate larger.Therefore, the bump electrode used in a semiconductor chip for an LCDdriver is much larger than general-purpose semiconductor chips.

In the LCD driver, an insulation film which functions as a surfaceprotection film (passivation film) is formed under the bump electrodeand the bump electrode is coupled with a pad formed in the top layer ofthe multilayer wiring layer through an opening made in the insulationfilm. Usually, the opening and pad are almost equal to the bumpelectrode in terms of area. However, when the pad is almost equal to thebump electrode, the pad occupies a large area and raises a problem thatno space is available for power lines and signal lines to be arranged inthe same layer as the pad.

For this reason, usually an LCD driver uses a pad which is smaller thana bump electrode. Since the bump electrode is larger than the pad, ithas an overlap region which overlaps the pad and a non-overlap regionwhich does not overlap it, in a plan view. Therefore, space is availablein the top layer of multilayer wiring layer under the non-overlap regionof the bump electrode. Consequently, power lines and signal lines can bedisposed in this space, permitting effective use of the space beneaththe non-overlap region. Thus, by using a pad smaller than a bumpelectrode, wirings can be disposed under the bump electrode in additionto the pad, contributing to size reduction of the semiconductor chip(LCD driver).

Nevertheless, the presence of wirings in the top wiring layer under thebump electrode poses a problem which is explained below referring todrawings. FIG. 36 shows the coupling relation between top layer wiringsand a bump electrode of a semiconductor chip which configures an LCDdriver. As shown in FIG. 36, a pad PD and wirings L1 and L2 are formedin the top layer of an interlayer insulation film 100. Namely, the padPD and wirings L1 and L2 are formed in the same layer. A surfaceprotection film 101 is formed so as to cover the top wiring layer inwhich the pad and wirings are formed. This surface protection film 101has an irregular surface which reflects the locations of the pad PD andwirings L1 and L2. Consequently, the bump electrode BP formed over thesurface protection film 101 has a form which reflects the irregularitiesof the surface protection film 101. This bump electrode BP iselectrically coupled with the pad PD through a plug SIL with aconductive material buried in its opening. The bump electrode BP, formedover the surface protection film 101, is larger than the pad PD and hasan overlap region X which overlaps the pad PD and a non-overlap region Ywhich does not overlap it, in a plan view. In other words, no pad PD isformed in the top wiring layer beneath the non-overlap region Y of thebump electrode BP shown in FIG. 36 and some space is available. Thisspace can be effectively used to dispose wirings L1 and L2 in the topwiring layer in addition to the pad PD so that the semiconductor chip(LCD driver) can be smaller.

However, if wirings L1 and L2 are disposed in the top wiring layer justbeneath the non-overlap region Y of the bump electrode BP,irregularities which reflect the locations of the wirings L1 and L2 aregenerated on the surface protection film 101. Consequently the bumpelectrode BP formed over the surface protection film 101 hasirregularities reflecting the irregularities of the film 101. If thebump electrode BP has such an irregular surface, there would be somedifficulty in mounting the semiconductor chip on a glass substrate.

FIG. 37 is a sectional view showing how the semiconductor chip ismounted on a glass substrate. As illustrated in FIG. 37, a semiconductorchip is mounted on a glass substrate 103 by coupling the bump electrodeBP of the semiconductor chip with the wiring 103 a of a glass substrate103 through an anisotropic conductive film ACF. If the bump electrode BPhas an irregular surface, conductive particles 102 of the ACF fail tocontact the bump electrode BP properly. As illustrated in FIG. 37, whilethe convex parts of the irregular surface of the bump electrode BPcontact conductive particles 102, the concave parts cannot contactconductive particles 102 properly. The convex parts of the bumpelectrode BP, which are subjected to the pressure of the glass substrate103, contact conductive particles 102, assuring electrical conductivity.On the other hand, the concave parts of the bump electrode BP are hardlysubjected to the pressure of the glass substrate 103, making itdifficult to assure electrical conductivity between the bump electrodeBP and conductive particles 102.

Therefore, even if the bump electrode BP size is increased to assureconductivity between the glass substrate 103 and bump electrode BPthrough the ACF, surface irregularities of the bump electrode BP makesit difficult to improve reliability in coupling between the bumpelectrode BP and the wiring 103 a formed over the glass substrate 103.

An object of the present invention is to provide a technique whichincreases reliability in coupling between the bump electrode of asemiconductor chip and the wiring of a mounting substrate. Moreparticularly it is intended to provide a technique which increasesreliability in coupling between a bump electrode and a wiring formedover a glass substrate by assuring the flatness of the bump electrodeeven when wirings lie in the top wiring layer under the bump electrode.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description in thisspecification and the accompanying drawings.

Preferred embodiments of the invention which will be disclosed hereinare briefly outlined below.

According to a preferred embodiment of the present invention, asemiconductor device comprises (a) a semiconductor substrate, (b) asemiconductor element formed over the semiconductor substrate, (c) amultilayer wiring layer formed over the semiconductor element, and (d) apad formed in the top layer of the multilayer wiring layer. It furthercomprises (e) a surface protection film which is formed over the pad andhas an opening which reaches the pad, and (f) a bump electrode which isformed over the surface protection film and electrically coupled withthe pad by filling the opening. The bump electrode is larger than thepad so as to have an overlap region which overlaps the pad in a planview and a non-overlap region which does not overlap the pad in a planview. Here, (g) a first wiring comprised of a power line or signal linein addition to the pad, and (h) a dummy pattern different from the firstwiring are formed in the top layer of the multilayer wiring layer. Thefirst wiring, formed in the same layer as the pad, is formed in thelayer under the non-overlap region of the bump electrode.

Since a dummy pattern lies in the top layer of the multilayer wiringlayer in addition to a power line or signal line, the flatness of thesurface protection film formed over the top layer is increased. If onlypower lines or signal lines are formed in the top layer of themultilayer wiring layer, surface irregularities caused by the power orsignal lines would be serious because the top layer cannot be denselyfilled with power or signal lines. On the other hand, by filling thelayer with dummy patterns as well as power or signal lines, the flatnessof the top layer is increased. Therefore, the flatness of the surfaceprotection film formed over the top layer is guaranteed and the flatnessof the bump electrode formed over the surface of the surface protectionfilm is also increased.

According to a preferred embodiment of the present invention, a methodof manufacturing a semiconductor device includes the steps of (a)forming a semiconductor element over a semiconductor substrate, (b)forming a multilayer wiring layer over the semiconductor element, and(c) forming a conductive film in the top layer of the multilayer wiringlayer. These steps are followed by the steps: (d) forming a pad, a firstwiring comprised of a power line or signal line, and a dummy pattern bypattering the conductive film, and (e) forming a surface protection filmso as to cover the pad, the first wiring and the dummy pattern. Themethod further includes the steps of (f) making in the surfaceprotection film an opening which reaches the pad, and (g) forming a bumpelectrode larger than the pad, over the surface protection filmincluding the opening. Here at the step (g) the bump electrode is formedso as to have an overlap region which overlaps the pad in a plan viewand a non-overlap region which does not overlap the pad in a plan view.The first wiring formed in the same layer as the pad is formed in thelayer under the non-overlap region of the bump electrode formed at thestep (g) and the dummy pattern is formed in a given area adjacent to thefirst wiring formed in the layer under the non-overlap region.

The advantageous effects brought about by preferred embodiments of thepresent invention disclosed herein are briefly described below.

Since a dummy pattern lies in the top layer of the multilayer wiringlayer in addition to a power line or signal line, the flatness of thesurface protection film formed over the top wiring layer is increased.If only power lines or signal lines are formed in the top layer of themultilayer wiring layer, surface irregularities caused by the power orsignal lines would be serious because the top layer cannot be denselyfilled with power or signal lines. By forming the layer with dummypatterns as well as power or signal lines, the flatness of the top layeris increased. Therefore, the flatness of the surface protection filmformed over the top layer is guaranteed and the flatness of the bumpelectrode formed over the surface of the surface protection film is alsoincreased. Consequently the reliability in coupling between the bumpelectrodes of the semiconductor chip and the wirings of the mountingsubstrate is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor chip according to an embodimentof the present invention;

FIG. 2 is an enlarged view showing bump electrodes for input signals andtheir vicinities in the semiconductor chip shown in FIG. 1;

FIG. 3 is an enlarged view showing an arrangement of dummy patternsshown in FIG. 2;

FIG. 4 is an enlarged view showing bump electrodes for input signals andtheir vicinities in the semiconductor chip shown in FIG. 1;

FIG. 5 is a sectional view taken along the line A-A in FIG. 2;

FIG. 6 is a sectional view taken along the line B-B in FIG. 2;

FIG. 7 illustrates the relation between the size of dummy patterns andthe irregular surface of the silicon oxide film covering the dummypatterns;

FIG. 8 illustrates the relation between the size of dummy patterns andthe irregular surface of the silicon oxide film covering the dummypatterns;

FIG. 9 is an enlarged view showing bump electrodes for output signalsand their vicinities in the semiconductor chip shown in FIG. 1;

FIG. 10 is a variation of what is shown in FIG. 9;

FIG. 11 is a sectional view taken along the line A-A in FIG. 9;

FIG. 12 shows that wirings and dummy patterns formed in the top wiringlayer occupy less than 70% of the semiconductor chip area;

FIG. 13 is a sectional view taken along the line A-A in FIG. 12;

FIG. 14 shows that wirings and dummy patterns formed in the top wiringlayer occupy 70% or more of the semiconductor chip area;

FIG. 15 is a sectional view taken along the line B-B in FIG. 14;

FIG. 16 illustrates the initial stage of etching where wirings and dummypatterns formed in the top wiring layer occupy less than 70% of thesemiconductor chip area;

FIG. 17 illustrates the final stage of etching where wirings and dummypatterns formed in the top wiring layer occupy less than 70% of thesemiconductor chip area;

FIG. 18 illustrates the initial stage of etching where wirings and dummypatterns formed in the top wiring layer occupy 70% or more of thesemiconductor chip area;

FIG. 19 illustrates the final stage of etching where wirings and dummypatterns formed in the top wiring layer occupy 70% or more of thesemiconductor chip area;

FIG. 20 is a sectional view of a MISFET formed in a semiconductor chip;

FIG. 21 is a flowchart showing the sequence of manufacturing a MISFET;

FIG. 22 is a sectional view showing a step in the process ofmanufacturing a semiconductor device in an embodiment;

FIG. 23 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 22;

FIG. 24 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 23;

FIG. 25 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 24;

FIG. 26 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 25;

FIG. 27 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 26;

FIG. 28 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 27;

FIG. 29 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 28;

FIG. 30 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 29;

FIG. 31 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 30;

FIG. 32 is a sectional view showing a semiconductor device manufacturingstep following the step shown in FIG. 31;

FIG. 33 is a sectional view showing that a semiconductor chip is mountedon a glass substrate in an embodiment;

FIG. 34 is an enlarged view showing that the semiconductor chip andglass substrate are coupled through an anisotropic conductive film;

FIG. 35 shows main components of a liquid crystal display device;

FIG. 36 shows the coupling relation between top layer wirings and a bumpelectrode of a semiconductor chip, based on the present inventors'examination; and

FIG. 37 is a sectional view showing how a semiconductor chip is mountedon a glass substrate, based on the present inventors' examination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments described below will be described separatelyas necessary, but they are not irrelevant to each other unless otherwisespecified. They are, in whole or in part, variations of each other andsometimes one description is a detailed or supplementary form ofanother.

Also, in the preferred embodiments described below, even when thenumerical datum for an element (the number of pieces, numerical value,quantity, range, etc.) is indicated by a specific numerical figure, itis not limited to the indicated specific numerical figure unlessotherwise specified or theoretically limited to the specific numericalfigure; it may be larger or smaller than the specific numerical figure.

In the preferred embodiments described below, it is needles to say thattheir constituent elements (including constituent steps) are notnecessarily essential unless otherwise specified or consideredtheoretically essential.

Likewise, in the preferred embodiments described below, when a specificform or positional relation is indicated for an element, it should beinterpreted to include forms or positional relations which are virtuallyequivalent or similar to the specific one unless otherwise specified orunless the specific one is considered to be necessary theoretically. Thesame can be said of numerical values or ranges as mentioned above.

In all the drawings that illustrate the preferred embodiments, elementswith like functions are basically designated by like reference numeralsand repeated descriptions thereof are omitted. For easy understanding,hatching may be used even in a plan view.

FIG. 1 is a plan view showing a semiconductor chip CHP (semiconductordevice) in an embodiment of the invention. The semiconductor chip CHP inthis embodiment is an LCD driver. Referring to FIG. 1, for example, thesemiconductor chip CHP includes a semiconductor substrate 1S which takesthe form of an elongated rectangle, and an LCD driver which drives anLCD device is formed on its main surface. This LCD driver has thefunction of controlling the orientations of liquid crystal molecules bysupplying voltage to each pixel in a cell array configuring the LCD andincludes a gate drive circuit, a source drive circuit, a liquid crystaldrive circuit, a graphic RAM (Random Access Memory), and a peripheralcircuit. The functions of these elements are performed by semiconductorelements and wirings formed over the semiconductor substrate 1S. First,the surface configuration of the semiconductor chip CHP will beexplained below.

The semiconductor chip CHP is a rectangle having a pair of short edgesand a pair of long edges where bump electrodes BP1 are arranged in a rowalong one of the long edges (lower edge as seen in FIG. 1). The bumpelectrodes BP1 function as external connection terminals for couplingwith an integrated circuit (LCD driver) including semiconductor elementsand wirings formed inside the semiconductor chip CHP. The bumpelectrodes BP1 are bump electrodes for digital input signals or analoginput signals.

Also, bump electrodes BP2 are arranged along the other long edge (upperedge as seen in FIG. 1). They are arranged in two rows in a zigzagpattern. This arrangement pattern permits the bump electrodes BP2 to bedensely located. These bump electrodes BP2 also function as externalconnection terminals which couple the integrated circuit inside thesemiconductor substrate 1S with the outside. The bump electrodes BP2 arebump electrodes for output signals from the LCD driver.

In this way, bump electrodes BP1 and bump electrodes BP2 are arrangedalong the pair of long edges on the periphery of the semiconductor chipCHP. The number of bump electrodes BP2 is larger than that of bumpelectrodes BP1; while the bump electrodes BP1 are disposed in line alongone long edge, the bump electrodes BP2 are disposed in a zigzag patternalong the other long edge. The reason for this arrangement is that thebump electrodes BP1 are for input signals which go into the LCD driverand the bump electrodes BP2 are for output signals which come from theLCD driver. Since input signals which go into the LCD driver carryserial data, not so many bump electrodes BP1 as external connectionterminals are required. On the other hand, output signals which comefrom the LCD driver carry parallel data and many bump electrodes BP2 asexternal connection terminals are required. More specifically, each ofthe bump electrodes BP2 for output signals is provided for a cellforming a liquid crystal display element (pixel), which means that asmany bump electrodes BP2 as cells are required. Therefore, the number ofbump electrodes BP2 for output signals is larger than that of bumpelectrodes BP1 for input signals. For this reason, the bump electrodesBP1 for input signals can be arranged in line along a long edge and thebump electrodes BP2 for output signals are arranged in a zigzag patternalong a long edge.

Although FIG. 1 shows that bump electrodes BP1 for input signals andbump electrodes BP2 for output signals are arranged along the pair oflong edges of the semiconductor chip CHP, bump electrodes arranged alongthe pair of short edges may be added to these.

Next, the bump electrodes BP1 and BP2 will be described in detail. Thebump electrodes BP1 and BP2 each take the form of a rectangle havingshort edges and long edges where their long edges are parallel to theshort edges of the semiconductor chip CHP and they are arranged alongthe long edges of the semiconductor chip CHP. The bump electrodes BP1and BP2 which are formed over the semiconductor chip CHP are larger insize (area) than general-purpose bump electrodes. In other words, thesurface area ratio of bump electrodes BP1 and BP2 is larger. As will bedescribed later, this is intended to assure coupling reliability inmounting the semiconductor chip CHP (LCD driver) on a glass substratefor a liquid crystal display device through an anisotropic conductivefilm. Therefore, while a general-purpose semiconductor chip does nothave bump electrodes in an active region in which a semiconductorelement is formed, a semiconductor chip CHP for an LCD driver has bumpelectrodes BP1 and BP2 in an active region.

Bump electrodes BP1 are formed over the surface of the semiconductorchip CHP. Next, an explanation will be given of the positional relationbetween bump electrodes BP1 and a top wiring layer under them. FIG. 2 isan enlarged view showing a region R in FIG. 1. Referring to FIG. 2, bumpelectrodes BP1 lie side by side along a long edge of the semiconductorchip. FIG. 2 shows two neighboring bump electrodes BP1. These bumpelectrodes BP1 are formed over the surface protection film (passivationfilm) of the semiconductor chip and a top wiring layer is formed underthe surface protection film. In FIG. 2, the surface protection film isomitted in order to illustrate the positional relation between the topwiring layer under the surface protection film and the bump electrodesBP1.

As shown in FIG. 2, the bump electrodes BP1 are coupled with pads PDformed in the top wiring layer. Each bump electrode BP1 is larger thanthe pad PD. In addition to the pad, a wiring L1 lies in the top wiringlayer under the bump electrode. Namely, the wiring L1 extends along thelong edge of the semiconductor chip CHP beneath the bump electrode BP1.Since the bump electrode BP1 is larger than the pad PD, some space isavailable in the top layer of the multilayer wiring layer beneath thebump electrode BP1. Therefore, the wiring L1 can be laid in this spacefor the effective use of the space beneath the bump electrode BP1. Thus,the use of the pad PD smaller than the bump electrode BP1 makes itpossible to lay the wiring L1 under the bump electrode BP1 in additionto the pad PD, so the semiconductor chip CHP (LCD driver) can besmaller. The wiring L1 may be a power line or signal line.

As explained earlier, when a wiring L1 is formed beneath a bumpelectrode BP1, the surface protection film has an irregular surfacereflecting the level difference between the wiring and the space; thusthe bump electrode BP1 will be formed over the irregular surface of thesurface protection film. As a consequence, the surface of the bumpelectrode BP 1 will be not flat but irregular. If the surface of thebump electrode BP1 is irregular, there will be some difficulty inmounting the semiconductor chip on the glass substrate. Thus the surfaceof the bump electrode BP1 must be flat.

In this embodiment, dummy patterns DP are formed in the top wiring layerin which wirings L1 lie, as shown in FIG. 2. In the example of FIG. 2,dummy patterns DP are laid in regions adjacent to the wirings L1 in away to fill the regions. Particularly the space between wirings L1 isfilled with dummy patterns DP. Consequently the space beneath each bumpelectrode BP1 is filled with dummy patterns DP. In other words, aplurality of wirings L1, and dummy patterns DP formed between wirings L1lie in the top wiring layer beneath the bump electrode BP1. This reducesthe level difference between wirings and space in the layer under thebump electrode BP1 (top wiring layer). More specifically, dummy patternsDP, which have almost the same height as the wirings L1, are formed inthe space available in the layer under the bump electrode BP1 (topwiring layer), so the level difference in the layer under the bumpelectrode BP1 (top wiring layer) is reduced by the wirings L1 and dummypatterns.

In the top wiring layer, in addition to the dummy patterns DP disposedparallel to the wirings L1 beneath the bump electrodes BP1, dummypatterns DP are formed in regions which are not beneath the bumpelectrodes BP1. Namely, dummy patterns DP are disposed adjacent to thewirings L1 in regions which do not overlap the bump electrodes in a planview. Formation of dummy patterns DP in the space beneath a bumpelectrode BP1 is considered necessary to eliminate the level differencebetween the wiring L1 beneath the bump electrode BP1 and the space. Thequestion is whether or not it is advantageous to form dummy patterns DPadjacent to the wirings L1 in regions which do not overlap the bumpelectrodes BP1 in a plan view. However, even in a region not beneath abump electrode BP1, there would be a level difference between a wiringL1 and space. If there should be this kind of level difference near abump electrode BP1, it would affect the flatness of the bump electrodeBP1. For this reason, in this embodiment, dummy patterns DP are laid notonly in the layer beneath the bump electrode BP1 (top wiring layer) butin a region within a given distance from the bump electrode BP1 toguarantee the flatness of the bump electrode BP1.

Next, the arrangement of dummy patterns DP will be described. FIG. 3shows an arrangement of dummy patterns DP. As illustrated in FIG. 3,each dummy pattern DP is a rectangle having short edges and long edgesand such dummy patterns DP are arranged vertically and horizontally asseen in the figure to fill the space. For example, each dumpy patternhas a long edge of 5.0 μm and a short edge of 0.8 μm. Since a wiring L1typically has a width of 20-30 μm, both the short edge and long edge ofthe dummy pattern DP are smaller than the width of the wiring L1. Namelyeach dummy pattern DP is very small. This means that even when the spacebetween wirings L1 is smaller than the width of the wiring L1, the smallspace can be filled with dummy patterns. Thus, since even a small spacecan be filled with dummy patterns DP, the flatness of the top wiringlayer can be high enough. Particularly, as illustrated in FIG. 3, eachdummy pattern itself is small and the interval between dummy patterns DPis, for example, as small as 0.6 μm. In other words, the intervalbetween dummy patterns DP is smaller than the short edge of the dummypattern DP so that the space is densely filled with dummy patterns.

FIG. 4 shows an example of arrangement of dummy patterns DP which isdifferent from the one shown in FIG. 2. As illustrated in FIG. 4, thelayer under bump electrodes BP1 (top wiring layer) is occupied by aplurality of wirings L1. In other words, wirings L1 are densely disposedand no space is available for dummy patterns DP in the layer under thebump electrodes BP1 (top wiring layer). Therefore, in the example ofFIG. 4, it seems that there is no problem of level difference in thelayer under bump electrodes BP1 (top wiring layer). However, asillustrated in FIG. 4, while wirings L1 are formed so as to fill theregions beneath the bump electrodes BP1, no wirings L1 are formed in theperipheral regions which do not overlap the bump electrodes BP1 in aplan view. Specifically, the peripheral regions of the bump electrodesBP1 include both regions with wirings L1 formed in the top wiring layerand regions without wirings (space). Thus, there will be a leveldifference between a wiring L1 and the space. For the purpose ofassuring the flatness of bump electrodes BP1, it is important to reducesuch a level difference beneath each bump electrode BP1. Since even alevel difference in the peripheral region of the bump electrode BP1affects the flatness of the bump electrode BP1, this level difference inthe peripheral region should also be reduced in the top wiring layer.This is because, in the example of FIG. 4, dummy patterns DP are alsoformed in regions adjacent to wirings L1 (peripheral regions of bumpelectrodes BP1). Consequently, level differences in the peripheralregions of bump electrodes BP1 are reduced in the top wiring layer andthe flatness of bump electrodes BP1 formed over the top wiring layer isguaranteed. As FIGS. 2 and 4 indicate, it is apparent that when thereare wirings L1 and space beneath a bump electrode BP1, it is mosteffective to form dummy patterns DP so as to fill the space and it isalso effective to form dummy patterns DP in the top wiring layer even ina peripheral region within a given distance from the bump electrode BP.The positional relation between bump electrodes BP1 and dummy patternsDP formed in the layer beneath bump electrodes BP1 (top wiring layer)has been explained above. The same is true of the positional relationbetween bump electrodes BP2 and dummy patterns DP.

Next, dummy patterns DP are explained referring to sectional views. FIG.5 is a sectional view taken along the line A-A in FIG. 2. FIG. 5 showsonly the multilayer wiring layer's upper part including the top wiringlayer and omits its part under the top wiring layer.

As illustrated in FIG. 5, a wiring 42 is formed over a silicon oxidefilm 40 as an interlayer insulation film. This wiring 42 is coupled witha wiring under it through a plug 43. Although wirings and asemiconductor element which are under the plug 43 formed in the siliconoxide film 40 are not shown in FIG. 5, a multilayer wiring and asemiconductor element like MISFET are formed under the wiring 42. Aninterlayer insulation film is formed in a way to cover the wiring 42.The interlayer insulation film is comprised of a silicon oxide film 20and a silicon oxide film 21 of TEOS (Tetra Ethyl Ortho Silicate) formedover the silicon oxide film 20. A top wiring layer is formed over theinterlayer insulation film. The top wiring layer includes a pad, wiringsL1 and dummy patterns DP. The pad PD, wirings L1 and dummy patterns DPare formed by patterning a conductive film and they have the samethickness. Namely the height of the wirings L1 is almost the same asthat of the dummy patterns DP. The pad PD is electrically coupled withthe wiring 42 by a plug 41 penetrating the silicon oxide film 20 andsilicon oxide film 21. In other words, the pad PD is electricallycoupled with the semiconductor element through the wiring 42 and wiringsunder it. A silicon oxide film 22 a is formed so as to cover the topwiring layer and a silicon oxide film 23 of TEOS is formed over thesilicon oxide film 22 a. Also a silicon nitride film 24 is formed overthe silicon oxide film 23. The silicon oxide film 22 a, silicon oxidefilm 23 and silicon nitride film 24 configure a surface protection film(passivation film). The surface protection film is intended to protectthe semiconductor chip from mechanical stress or impurities. Therefore,the surface protection film is required to function as a barrier againstmechanical strength or polluting impurities such as mobile ions. Forexample, as illustrated in FIG. 5, it is a laminate comprised of thesilicon oxide film 22 a, silicon oxide film 23 and silicon nitride film24.

An opening 25 which reaches the pad PD is made in the surface protectionfilm and a plug SIL is formed by burying a conductive material in theopening 25. A bump electrode BP1 which is electrically coupled with theplug SIL is formed over the surface protection film. The bump electrodeBP1 is, for example, comprised of a UBM (Under Bump Metal) film 26 and agold film 28.

The bump electrode BP1, larger than the pad PD, extends over the surfaceprotection film. Therefore, in a plan view, the bump electrode BP1 hasan overlap region X which overlaps the pad PD and a non-overlap region Ywhich does not overlap the pad. Wirings L1 lie in the layer under thenon-overlap region Y (top wiring layer). Also a dummy pattern DP liesbetween the wirings L1. Therefore, if only wirings L1 lie in the layerunder the non-overlap region Y (top wiring layer), irregularities due tothe level difference between the wirings L1 and space would be generatedand the surface protection film, reflecting the level difference, wouldbe irregular. As a consequence, the surface of the bump electrode BP1formed over the surface protection film would be irregular. However, inthis embodiment, dumpy patterns DP which have the same height as thewirings L1 are formed so as to fill the space between wirings L1, solevel differences in the layer under the non-overlap region Y (topwiring layer) can be reduced. Therefore the flatness of the surfaceprotection film formed over the top wiring layer is improved and theflatness of the bump electrode BP1 formed over the surface protectionfilm is also improved.

In sum, one feature of this embodiment (first feature) is that wiringsL1 and dummy patterns DP are formed in the layer under the non-overlapregion Y (top wiring layer) of a bump electrode BP1 and the dummypatterns have the same height as the wirings L1 and lie in the spacebetween wirings L1, thereby reducing level differences in the top wiringlayer. As a consequence, the flatness of the bump electrode BP1 isincreased. Therefore, in this embodiment, wirings L1 (power lines orsignal lines) can be disposed in the layer under the non-overlap regionY (top wiring layer) of the bump electrode BP1, so the region beneath alarge bump electrode BP1 can be effectively used. Furthermore,deterioration in the flatness of the bump electrode BP1 which may becaused by the presence of wirings L1 in the layer under the non-overlapregion Y (top wiring layer) is alleviated by filling the space betweenwirings L1 with dummy patterns DP. As explained above, according to thisembodiment 1, the semiconductor chip can be smaller and the flatness ofthe bump electrode BP1 can be increased, so the reliability in couplingbetween the semiconductor chip and substrate can be increased.

Another feature of the embodiment (second feature) is that the surfaceprotection film is flattened. As described above, dummy patterns DP areformed along with wirings L1 in the top wiring layer to reduceirregularities in the top wiring layer. However, as shown in FIG. 5,some irregularities will remain on the silicon oxide film 22 a formed soas to cover the top wiring layer. In order to make the surfaceprotection film flatter, the silicon oxide film 23 of TEOS is formedover the silicon oxide film 22 a. The surface of the silicon oxide film23 is flattened by chemical mechanical polishing (CMP). Thus the surfaceof the silicon oxide film 23 as part of the surface protection film isflattened. In sum, after the silicon oxide film 22 a is formed over thetop wiring layer, the silicon oxide layer 23 is formed over the siliconoxide film 22 a and its surface is flattened to increase the flatness ofthe surface protection film. Since the silicon nitride film 24 is formedover the silicon oxide film 23 which has been flattened by CMP, it isalso flat. Thus the flatness of the surface protection film covering thetop wiring layer is surely increased. As a consequence, the bumpelectrode BP1 is formed over the flattened surface protection film andthe flatness of the bump electrode BP1 is guaranteed. Since the surfaceof the surface protection film is the silicon nitride film 24, it may bepossible to polish the surface of not the silicon oxide film 23 but thesilicon nitride film 24 by CMP. However, because of its nature, thesilicon nitride film 24 is not suitable to be polished by an ordinaryCMP process. For this reason, the surface of the silicon oxide film 23underlying the silicon nitride film 24 is flattened by CMP. In otherwords, since the silicon oxide film 23 is easy to polish by CMP, thesurface protection film is flattened by flattening the silicon oxidefilm 23.

As described above, in this embodiment, the first feature that the topwiring layer is filled with dummy patterns DP and the second featurethat the surface protection film covering the top wiring layer isflattened by CMP are combined to ensure that the bump electrode BP1formed over the surface protection film is flattened. However, it is notindispensable to combine the first feature and the second feature; thebump electrode BP1 is flattened by adopting either the first feature orthe second feature.

FIG. 6 is a sectional view taken along the line B-B in FIG. 2. Asillustrated in FIG. 6, dummy patterns DP in the top wiring layer aredisposed in line along the array of bump electrodes BP1. These dummypatterns DP extend in the same direction as wirings L1 (not shown inFIG. 6) but they are an array of dummy patterns unlike the wirings L1which are each a single line. Each dummy pattern DP is a small rectanglewhose short edges and long edges are smaller than the width of eachwiring L1. The space in the top wiring layer is filled with such smallrectangular dummy patters D1.

The use of small rectangular dummy patterns offers two advantages whichwill be explained below. The first advantage is that the space in thetop wiring layer can be filled adequately regardless of space size. Morespecifically, a plurality of wirings L1 are formed in the top wiringlayer and the interval between certain neighboring wirings L1 is largerthan that that between other ones. If the dummy pattern size is as largeas the width of wiring L1, a narrow interval between wirings cannot befilled with dummy patterns DP. On the other hand, if the short and longedges of a dummy pattern DP are both smaller than the width of wiringL1, even a relatively small interval (space) can be filled with dummypatterns DP. Thanks to the smallness of the dummy pattern DP, variousforms of space can be filled with dummy patterns without the need forchanging the dummy pattern form.

The second advantage of small dummy patterns DP is as follows. Forexample, if the dummy pattern size is larger and the interval betweendummy patterns DP is wider as shown in FIG. 7, the depth S1 of surfaceirregularity of the silicon oxide film 22 a formed to cover the dummypatterns DP is larger. This is not desirable from the viewpoint that thepurpose of dummy patterns DP in the top wiring layer is to reduceirregularities in the top wiring layer. On the other hand, as shown inFIG. 8, if the dummy pattern size is small and the interval betweendummy patterns DP is narrower, the depth S2 of surface irregularity ofthe silicon oxide film 22 a formed to cover the dummy patterns DP issmaller. This is desirable from the viewpoint that the purpose of dummypatterns DP in the top wiring layer is to reduce irregularities in thetop wiring layer. Thus, smaller dummy patterns DP and a narrowerinterval between dummy patterns DP are better for the purpose ofincreasing the bump electrode flatness.

The positional relation between the bump electrodes BP1 for inputsignals and the top wiring layer in the semiconductor chip has beenexplained so far. Next, the positional relation between the bumpelectrodes BP2 for output signals and the top wiring layer will beexplained. The positional relation between the bump electrodes BP2 foroutput signals and the top wiring layer is similar to that between thebump electrodes BP1 for input signals and the top wiring layer.

FIG. 9 is an enlarged view of a corner of the semiconductor chip and itsvicinity. In FIG. 9, the horizontal direction represents the long edgedirection of the semiconductor chip CHP and the vertical directionrepresents the short edge direction of the chip. As illustrated here,bump electrodes BP2 for output signals are disposed in line along thelong edge direction of the semiconductor chip CHP. Particularly, thebump electrodes BP2 for output signals are arranged in two rows in azigzag pattern. This arrangement permits many bump electrodes BP2 to liedensely along the long edge direction of the chip CHP.

Each bump electrode BP2 takes the form of a rectangle having short edgesand long edges and a pad PD lies in the top wiring layer under part ofthe bump electrode BP2. The pad PD and the bump electrode BP areelectrically coupled by a plug SIL. In this embodiment, the bumpelectrode BP2 is larger than the pad and plug and is coupled with thepad PD, smaller than the bump electrode BP2, by the plug SIL, smallerthan the pad PD. However, the short edge of the bump electrode BP2 isshorter than the pad PD. This is because, if the short edge of the bumpelectrode BP2 should be longer than the pad PD, the vicinity of theshort edge of the bump electrode BP2 would have an irregular surface asa reflection of the level difference between the pad area and non-padarea in the top wiring layer. Therefore, for the purpose of assuring theflatness of the vicinity of the short edge of the bump electrode BP2, itis desirable that the whole short edge of the bump electrode BP2 be overthe pad PD.

In addition to the pad PD, wirings L1 and dummy patterns DP under thelong edge of each bump electrode BP2. The long edge of the bumpelectrode BP2 is far longer than the pad PD, which means that there issome space beneath the bump electrode BP2 in the top wiring layer.Again, wirings L1 are laid under the bump electrode BP2 for outputsignals in order to effectively use the space available in the topwiring layer. These wirings L1 are, for example, power lines or signallines. They lie just beneath bump electrodes BP2 and extend along thelong edge of the semiconductor chip CHP along which bump electrodes BP2are disposed in rows.

When a wiring L1 is formed beneath a bump electrode BP1 in this way, thesurface protection film has an irregular surface reflecting the leveldifference between the wiring and the space; thus the bump electrode BP1will be formed over the irregular surface of the surface protectionfilm. As a consequence, the surface of the bump electrode BP 2 will benot flat but irregular. If the surface of the bump electrode BP2 isirregular, there will be some difficulty in mounting the semiconductorchip on the glass substrate. Thus the surface of the bump electrode BP2must be flat.

Therefore, in this embodiment, dummy patterns DP are formed beneath bumpelectrodes BP2 for output signals in the top wiring layer in whichwirings L1 lie, as in the case of bump electrodes BP1 for input signals.In the example of FIG. 9, dummy patterns DP are laid in regions adjacentto wirings L1 in a way to fill the regions. Particularly the spacebetween wirings L1 is filled with dummy patterns DP. Consequently thespace beneath each bump electrode BP1 is filled with dummy patterns DP.In other words, a plurality of wirings L1, and dummy patterns DP formedbetween wirings L1 lie in the top wiring layer beneath the bumpelectrode BP2. This reduces the level difference between wirings andspace in the layer under the bump electrode BP2 (top wiring layer). Morespecifically, dummy patterns DP, which have almost the same height asthe wirings L1, are formed in the space available in the layer under thebump electrode BP2 (top wiring layer), so the level difference in thelayer under the bump electrode BP2 (top wiring layer) is reduced by thewirings L1 and dummy patterns.

FIG. 10 shows an example of arrangement of dummy patterns DP which isdifferent from the one shown in FIG. 9. As illustrated in FIG. 10, thelayer under bump electrodes BP2 (top wiring layer) is occupied by aplurality of wirings L1. In other words, wirings L1 are densely disposedand no space is available for dummy patterns DP in the layer under thebump electrodes BP2 (top wiring layer). Therefore, in the example ofFIG. 10, it seems that there is no problem of level difference in thelayer under bump electrodes BP2 (top wiring layer). However, asillustrated in FIG. 10, while wirings L1 are formed so as to fill theregion beneath the bump electrodes BP2, no wirings L1 are formed in theperipheral regions which do not overlap the bump electrodes BP2 in aplan view. Specifically, the peripheral regions of the bump electrodesBP2 include both regions with wirings L1 formed in the top wiring layerand regions without wirings (space). Thus, there will be a leveldifference between wiring L1 and the space. For the purpose of assuringthe flatness of bump electrodes BP2, it is important to reduce such alevel difference beneath each bump electrode BP2. Since even a leveldifference in the peripheral region of the bump electrode BP2 affectsthe flatness of the bump electrode BP2, this level difference in theperipheral region of the bump electrode BP2 should also be reduced inthe top wiring layer. This is because, in the example of FIG. 10, dummypatterns DP are also formed in regions adjacent to wirings L1(peripheral regions of bump electrodes BP2). Consequently, leveldifferences in the peripheral regions of the bump electrodes BP2 arereduced in the top wiring layer and the flatness of bump electrodes BP2formed over the top wiring layer is guaranteed.

FIG. 11 is a sectional view taken along the line A-A in FIG. 9. As shownin FIG. 11, wiring 42 is formed over a silicon oxide film 40 as aninterlayer insulation film. This wiring 42 is coupled with wiring underit through a plug 43. Although wirings and a semiconductor element whichare under the plug 43 formed in the silicon oxide film 40 are not shownin FIG. 11, a multilayer wiring and a semiconductor element like MISFETare formed under the wiring 42. An interlayer insulation film is formedin a way to cover the wiring 42. The interlayer insulation film iscomprised of a silicon oxide film 20 and a silicon oxide film 21 of TEOS(Tetra Ethyl Ortho Silicate) formed over the silicon oxide film 20. Atop wiring layer is formed over the interlayer insulation film. The topwiring layer includes pads PD, wirings L1 and dummy patterns DP. Thepads PD, wirings L1 and dummy patterns DP are formed by patterning aconductive film and they have the same thickness. Namely the height ofthe wirings L1 is almost the same as that of the dummy patterns DP. Eachpad PD is electrically coupled with the wiring 42 by a plug 41penetrating the silicon oxide film 20 and silicon oxide film 21. Inother words, the pad PD is electrically coupled with the semiconductorelement through the wiring 42 and wirings under it. A silicon oxide film22 a is formed so as to cover the top wiring layer and a silicon oxidefilm 23 of TEOS is formed over the silicon oxide film 22 a. Also asilicon nitride film 24 is formed over the silicon oxide film 23. Thesilicon oxide film 22 a, silicon oxide film 23 and silicon nitride film24 configure a surface protection film (passivation film).

An opening 25 which reaches the pad PD is made in the surface protectionfilm and a plug SIL is formed by burying a conductive material in theopening 25. A bump electrode BP1 which is electrically coupled with theplug SIL is formed over the surface protection film. The bump electrodeBP2 is, for example, comprised of a UBM (Under Bump Metal) film 26 and agold film 28.

The bump electrode BP2, larger than the pad PD, extends over the surfaceprotection film. Therefore, in a plan view, the bump electrode BP2 hasan overlap region X which overlaps the pad PD and a non-overlap region Ywhich does not overlap the pad. Wirings L1 lie in the layer under thenon-overlap region Y (top wiring layer). Also a dummy pattern DP liesbetween wirings L1. Therefore, if only wirings L1 lie in the layer underthe non-overlap region Y (top wiring layer), irregularities due to thelevel difference between wirings L1 and space would be generated and thesurface protection film, reflecting the level difference, would beirregular. As a consequence, the surface of the bump electrode BP2formed over the surface protection film would be irregular. However, inthis embodiment, dumpy patterns DP which have the same height as thewirings L1 are formed so as to fill the space between wirings L1, solevel differences in the layer under the non-overlap region Y (topwiring layer) can be reduced. Therefore, the flatness of the protectionfilm formed over the top wiring layer is improved and the flatness ofthe bump electrode BP2 formed over the surface protection film is alsoimproved.

Furthermore, one feature of this embodiment is that the surfaceprotection film formed under bump electrodes BP2 for output signals isflattened. For example, the surface of the silicon oxide film 23 as partof the surface protection film is flattened by chemical mechanicalpolishing (CMP) or a similar technique. The surface of the silicon oxidefilm 23 is thus flattened. In sum, after the silicon oxide film 22 a isformed over the top wiring layer, the silicon oxide layer 23 is formedover the silicon oxide film 22 a and its surface is flattened toincrease the flatness of the surface protection film. Since the siliconnitride film 24 is formed over the silicon oxide film 23 which has beenflattened by CMP, it is also flat. Thus the flatness of the surfaceprotection film covering the top wiring layer is surely increased. As aconsequence, the bump electrode BP2 is formed over the flattened surfaceprotection film and the flatness of the bump electrode BP2 is thusguaranteed.

Thus, this embodiment has the first feature that the top wiring layerunder bump electrodes BP2 for output signals is also filled with dummypatterns DP and the second feature that the surface protection filmcovering the top wiring layer is flattened by CMP.

The first feature of this embodiment is that dummy patterns DP areformed both beneath bump electrodes BP1 for input signals and beneathbump electrodes BP2 for output signals. As a consequence, the space inthe top wiring layer is filled with dummy patterns and the surfaceprotection film covering the top wiring layer has a higher degree offlatness, resulting in a higher degree of flatness of bump electrodesBP1 and BP2 formed over the surface protection film.

Therefore, from the viewpoint that the level differences between thewirings L1 in the top wiring layer and the space between wirings L1should be eliminated, it may be desirable that dummy patterns DP beformed all over the semiconductor chip. In other words, for the purposeof increasing the flatness of the surface protection film covering thetop wiring layer and the flatness of bump electrodes BP1 formed over thesurface protection film, it may be desirable that dummy patterns beformed so as to fill the whole space in the top wiring layer.

However, in this embodiment, dummy patterns DP are not formed throughoutthe top wiring layer. For example, FIG. 1 shows that the top wiringlayer of the semiconductor chip CHP includes dummy pattern regions DRwhere dummy patterns are formed and a non-dummy pattern region NDR wheredummy patterns are not formed. The dummy pattern regions are formedwithin a given distance from bump electrodes BP1 and BP2. This isbecause, in order to achieve the flatness of bump electrodes BP1 andBP2, level differences in the top wiring layer which would directlyaffect the flatness of the bump electrodes BP1 and BP2 are eliminated byforming dummy patterns at least just beneath the bump electrodes BP1 andBP2 and in their peripheral regions. In short, for achieving theflatness of bump electrodes BP1 and BP2, it is not necessary to fill thewhole space in the top wiring layer with dummy patterns. In other words,the nun-dummy pattern region NDR does not affect the flatness of bumpelectrodes BP1 and BP2.

In this embodiment, dummy pattern regions DR are not provided all overthe semiconductor chip CHP surface for the following reasons. The firstreason is for the sake of convenience for semiconductor chip defectanalysis. The LCD driver semiconductor chips CHP shipped as products mayinclude some defective products. Defective products are collected fromcustomers and subjected to defect analysis. If dummy patterns are formedin the whole space in the top wiring layer, the inside of thesemiconductor chip is shielded by the metal film used in dummy patterns.A semiconductor element and multilayer wiring are formed inside thesemiconductor chip CHP. When defect analysis is to be made on thesemiconductor element and multilayer wiring, dummy patterns in the topwiring layer may hamper such defect analysis. For this reason, dummypatterns are not formed all over the top wiring layer. Therefore, dummypatterns are formed within a given distance from the bump electrodes BP1and BP2. Concretely, dummy pattern regions DR are within 70 μm from bumpelectrodes BP1 and BP2 and the rest is a non-dummy pattern region NDRwhere no dummy patterns are formed, thereby contributing to conveniencefor defect analysis. In other words, in this embodiment, the flatness ofbump electrodes BP1 and BP2 is increased by forming dummy patterns onlyin regions which affect the flatness of bump electrodes BP1 and BP2(part of the top wiring layer) and the convenience for defect analysisis enhanced by not forming dummy patterns in the other regions.

The second reason that dummy pattern regions DR are not formed all overthe semiconductor chip CHP surface is as follows. FIG. 12 shows a casethat the wirings L1 and dummy patterns DP formed in the top wiring layerof the semiconductor chip CHP occupy less than 70% of the layer. NamelyFIG. 12 shows a case that the ratio of dummy patterns DP in the topwiring layer is relatively low. FIG. 13 is a fragmentary sectional viewtaken along the line A-A in FIG. 12 showing a dummy pattern formingprocess. As illustrated in FIG. 13, a conductive film, from whichwirings L1 and dummy patterns DP are formed, lies over the silicon oxidefilm 21 as an interlayer insulation film and a patterned resist film RFis formed over the conductive film. Resist film patterning is done sothat resist film is left in regions where wirings L1 and dummy pattersDP are to be formed. Wirings L1 and dummy patterns DP are formed byetching the conductive film using the patterned resist film RF as amask. When the ratio of dummy patterns DP is as low as less than 70%,the ratio of conductive film removed by etching is high. This means thatthe area to be etched is large. When the area to be etched is large, itis easy to detect when etching is ended. Therefore, the end of etchingcan be detected accurately, which makes it easy to shape wirings L1 anddummy patterns DP accurately.

Next, an explanation will be given of a case that the wirings L1 anddummy patterns DP formed in the top wiring layer of the semiconductorchip CHP occupy 70% or more. FIG. 14 shows a case that the wirings L1and dummy patterns DP formed in the top wiring layer of thesemiconductor chip CHP occupy 70% or more. Namely, FIG. 14 shows a casethat the ratio of dummy patterns DP in the top wiring layer isrelatively high. FIG. 15 is a fragmentary sectional view taken along theline B-B in FIG. 14 showing a dummy pattern forming process.

As illustrated in FIG. 15, a conductive film, from which wirings L1 anddummy patterns DP are formed, lies over the silicon oxide film 21 as aninterlayer insulation film and a patterned resist film RF is formed overthe conductive film. Resist film patterning is done so that resist filmis left in regions where wirings L1 and dummy patters DP are to beformed. Wirings L1 and dummy patterns DP are formed by etching theconductive film using the patterned resist film RF as a mask. When theratio of dummy patterns DP is relatively high or 70% or more, the ratioof conductive film removed by etching is low. This means that the areato be etched is small. If the area to be etched is small, there is aproblem that the end of etching cannot be detected accurately. Thisproblem may arise in common etching equipment. In common etchingequipment, accuracy in detection of the end of etching varies dependingon the size of the area to be etched.

If the area to be etched is small and the end of etching cannot bedetected accurately, defective wiring patterns L1 and defective dummypatterns DP may be produced due to under-etching or over-etching. Onesolution to this problem may be to detect the end of etching, not basedon the actual etching condition but by controlling etching time.However, dimensional fluctuations in etching results cannot be properlyavoided by control of etching time. For this reason, detection of theend of etching should be not by an indirect method such as control ofetching time but based on the actual etching condition. Hence, for thepurpose of increasing the accuracy in detecting the end of etching toimprove the dummy pattern forming accuracy, dummy pattern regions DR asshown in FIG. 1 should not be formed all over the semiconductor chip CHPsurface and the ratio of the area occupied by dummy patterns in the topwiring layer should be low.

The second reason is further detailed below. FIG. 16 shows the processof etching the conductive film 22 formed over the silicon oxide film 21to form wirings and dummy patterns which configure the top wiring layer.FIG. 16 shows a case that the ratio of the area occupied by dummypatterns is less than 70% or the etched area of the conductive film 22is relatively large. For etching of the conductive film 22, chlorine gassuch as BCl₃ or Cl₃ is used as an etching gas. Here, etching is done bychemical reaction between the chlorine gas and the aluminum film of theconductive film 22. In this process, as the reaction product evaporates,the aluminum film is gradually removed. When a sufficient amount ofaluminum film exists, chemical reaction between the aluminum film andetching gas proceeds smoothly. Hence a large volume of reaction productis generated. The progress of aluminum film etching can be estimated bydetecting light emission (plasma emission) from the reaction product.More specifically, at the initial stage of etching, a sufficient amountof aluminum exists and chemical reaction between the aluminum film andetching gas proceeds smoothly and a large volume of reaction product isgenerated. Therefore, at the initial stage of etching, a large quantityof light is emitted from the reaction product due to the presence of alarge volume of reaction product.

FIG. 17 shows the final stage of etching where etching has been finishedafter the stage shown in FIG. 16. As illustrated in FIG. 17, patterningof the conductive film 22 has been almost finished and etching of thealuminum film of the conductive film 22 has been finished. At this time,since little aluminum film is left, chemical reaction between thealuminum film and etching gas is far less than in the initial stageshown in FIG. 16. Consequently the volume of reaction product fromchemical reaction between the aluminum film and etching gas is small andthe quantity of light emitted from the reaction product is also small.Namely the quantity of light emitted from the reaction product is smallat the final stage of etching. Therefore, the end of etching can bedetected by monitoring the quantity of light emitted from the reactionproduct in the etching process. When the quantity of light emitted fromthe reaction product becomes below a prescribed level, it may be decidedthat etching has been ended. If the etched area is large as shown inFIGS. 16 and 17, the difference in the intensity of light between theinitial stage and final stage of etching is large and the end of etchingcan be detected accurately.

Next, FIG. 18 shows a case that the ratio of the area occupied by dummypatterns is 70% or more, or the area of the conductive film 22 to beetched is relatively small. In this case, as illustrated in FIG. 18,since the area to be etched is small, the intensity of emitted light islow even at the initial stage of etching. More specifically, at theinitial stage of etching, a sufficient amount of conductive film is leftbut the area to be etched which is not covered by the resist film RF isvery small; thus chemical reaction between the aluminum film and etchinggas is less than when the ratio of the area occupied by dummy patternsis less than 70%. For the above reason, even at the initial stage ofetching, the volume of reaction product is small and the intensity oflight emitted from the reaction product is low.

Then, etching proceeds and comes to an end. FIG. 19 shows the finalstage of etching where etching has been finished after the stage shownin FIG. 18. As illustrated in FIG. 19, almost all the aluminum film ofthe conductive film to be etched is removed and chemical reactionbetween the aluminum film and etching gas is less active and the volumeof reaction product is small. Thus the intensity of light emitted fromthe reaction product is weak. When the ratio of the area occupied bydummy patterns is 70% or more as illustrated in FIGS. 18 and 19, thearea to be etched is small and the volume of reaction product frometching is small even at the initial stage of etching and thus thequantity (intensity) of light is small (low). This means that when theratio of the area occupied by dummy patterns is 70% or more, there islittle difference in the intensity of light between the initial andfinal stages of etching. Hence, it is difficult to detect the end ofetching accurately. If the end of etching is not detected accurately,there arises a problem that defective wiring patterns and defectivedummy patterns may be produced due to under-etching or over-etching. Forthe above reason, it is desirable to avoid forming too many dummypatterns in the top wiring layer. In sum, for the purpose of increasingthe accuracy in detecting the end of etching to improve the dummypattern forming accuracy, dummy pattern regions DR as shown in FIG. 1should not be formed all over the semiconductor chip CHP and the ratioof the area occupied by dummy patterns in the top wiring layer should below.

The conductive film 22 is comprised of an aluminum film sandwiched by anupper titanium/titanium nitride film and a lower one. Usually, etchingof the titanium/titanium nitride film is controlled according not to theemitted light intensity of reaction product but to etching time. Hence,if the end of etching of the aluminum film is detected accurately, thetitanium/titanium nitride film can be removed properly in a prescribedetching time; on the other hand, if the end of its etching is notdetected accurately, under-etching or over-etching of the aluminum filmwill occur, namely when etching is done for a prescribed time,under-etching or over-etching of the titanium/titanium nitride film mayoccur. This suggests that in order to process the conductive film 22accurately, it is important to detect the end of etching accurately.

For the above reasons, the ratio of dummy pattern regions in the topwiring layer is limited to a value required to flatten bump electrodes.In other words, the disadvantages entailed by formation of too manydummy patterns in the top wiring layer are avoided.

The features of this embodiment are briefly summarized as follows. Thefirst feature is to form dummy patterns in the top wiring layer and thesecond feature is to flatten the surface protection film covering thetop wiring layer by CMP. Concretely dummy patterns are formed onlybeneath bump electrodes and in their peripheral regions or to the extentrequired to implement the first feature in order to eliminate leveldifferences which would directly affect the flatness of bump electrodes.

The technical idea of this embodiment (first feature) is formation ofdummy patterns in the top wiring layer. In ordinary semiconductordevices, dummy patterns are formed in an intermediate wiring layer ofmultilayer wiring layer. This is because another wiring layer must bemade above the intermediate layer of the multilayer wiring layer and theintermediate layer must be flattened. However, the related art does nothave the technical idea that dummy patterns are formed in the top wiringlayer. Since there is no need to form a wiring layer above the topwiring layer, there is no idea that level differences caused by wiringsin the top wiring layer must be reduced. Namely, there has been no needto flatten the top wiring layer accurately.

On the other hand, the semiconductor device in this embodiment isassumed to be an LCD driver. The LCD driver is characterized in thatlarge bump electrodes are formed in the top wiring layer through thesurface protection film. In this case, wirings are disposed beneathlarge bump electrodes for the effective use of the layer under the bumpelectrodes (top wiring layer). Thus wirings and space are formed in thetop wiring layer beneath the bump electrodes and level differencesbetween the wirings and space are generated. These level differences arereflected in the surface protection film covering the top wiring layer,resulting in irregularities in the surface of the surface protectionfilm. Since the bump electrodes formed over the surface protection filmare large, the surfaces of the bump electrodes are also irregular as areflection of the irregular surface of the surface protection film. As asolution to this problem, in this embodiment, dummy patterns are formedin the top wiring layer to assure the surface flatness of bumpelectrodes (first feature). Therefore, the technical idea of the relatedart that dummy patterns are formed in an intermediate layer is differentfrom that of this embodiment in terms of premises and objective. Therelated art, which just suggests formation of dummy patterns in anintermediate layer, does not include an idea which motivates those inthe art to conceive of the first feature of this embodiment.

The second feature (technical idea) of this embodiment is to flatten thesurface protection film covering the top wiring layer by CMP. Thetechnique that the surface of an intermediate layer of the multilayerwiring layer is polished by CMP has been commonly used because there isneed to flatten the interlayer insulation film in order to form anotherwiring layer over an intermediate layer. However, this related art doesnot include an idea that the surface protection film formed so as tocover the top wiring layer should be flattened. This is because there isno need to form an wiring layer over the surface protection film andthus there is no need to flatten the surface protection film.

On the other hand, the semiconductor device in this embodiment isassumed to be an LCD driver. The LCD driver is characterized in thatlarge bump electrodes are formed in the top wiring layer through thesurface protection film. In this case, wirings are disposed beneathlarge bump electrodes for the effective use of the layer under the bumpelectrodes (the top wiring layer). Thus wirings and space are formed inthe top wiring layer beneath the bump electrodes and level differencesbetween the wirings and space are generated. These level differences arereflected in the surface protection film covering the top wiring layer,resulting in irregularities in the surface of the surface protectionfilm. Since the bump electrodes formed over the surface protection filmare large, the surfaces of the bump electrodes are also irregular as areflection of the irregular surface of the surface protection film. As asolution to this problem, in this embodiment, the surface of the surfaceprotection film is flattened by CMP. Therefore, the technical idea ofthe related art that the interlayer insulation film surface is flattenedby CMP is different from that of this embodiment in terms of premisesand objective. The related art, which just suggests flattening of anintermediate layer by CMP, does not include an idea which motivatesthose in the art to conceive of the second feature of this embodiment.

The features of this embodiment have been described above. Thisembodiment is characteristic in the semiconductor chip's top wiringlayer and its surface protection film lying over the top wiring layer.Wirings are formed in the layer under the top wiring layer of thesemiconductor chip and a semiconductor element is formed over asemiconductor substrate under the wirings. The semiconductor chip inthis embodiment is an LCD driver. The LCD driver has the function ofconverting input signals (serial data) into output signals (paralleldata) and the function as a level shift circuit which changes thevoltage value inside the LCD driver to apply a specified level ofvoltage to liquid crystal display elements (pixels). These LCD driverfunctions are performed by CMISFETs (Complementary Metal InsulatorSemiconductor Field Effect Transistors) formed in the semiconductorchip. There are two types of CMISFETs for use in the LCD driver:low-voltage MISFETs which operate at a relatively low voltage andhigh-voltage MISFETs which operate at a relatively high voltage. Next, aCMISFET and its first wiring layer will be described.

FIG. 20 is a sectional view of a CMISFET formed in a semiconductor chipin this embodiment. As illustrated in FIG. 20, element isolation regions2 are formed in the surface of a silicon monocrystal semiconductorsubstrate 1S. Active regions which configure a semiconductor element areseparated by an element isolation region 2. Among active regionsseparated by element isolation regions 2, a p-type well 3 a is formed inan n-channel MISFET formation region and an n-type well 3 b is formed ina p-channel MISFET formation region.

An n-channel MISFET is formed over the p-type well 3 a and a p-channelMISFET is formed over the n-type well 3 b. First, the n-channel MISFETis described. The n-channel MISFET has a gate insulation film 4 over thep-type well 3 a and a gate electrode 6 a is formed over the gateinsulation film 4. The gate electrode 6 a is a laminate comprised of apolysilicon film 5 and a cobalt silicide film 12 formed over thepolysilicon film 5. The cobalt silicide film 12 is formed in order todecrease the resistance of the gate electrode 6 a.

Side walls 9 are formed on both sides of the gate electrode 6 a and ashallow low-concentration n-type impurity diffusion region 7 is formedin the semiconductor substrate 1S just beneath each side wall 9. Thisshallow low-concentration n-type impurity diffusion region 7 is asemiconductor region in which n-type impurities such as phosphor andarsenic are introduced in the semiconductor substrate 1S and it isformed in a way to match the gate electrode 6 a. In the semiconductorsubstrate 1S, a deep high-concentration n-type impurity diffusion region10 is formed outside the shallow low-concentration n-type impuritydiffusion region 7. This deep high-concentration n-type impuritydiffusion region 10 is also a semiconductor region in which n-typeimpurities such as phosphor and arsenic are introduced in thesemiconductor substrate 1S and it is formed in a way to match the sidewall 9.

The shallow low-concentration n-type impurity diffusion region 7 anddeep high-concentration n-type impurity diffusion region 10 configure asource region and a drain region for an n-channel MISFET. When a shallowlow-concentration n-type impurity diffusion region 7 and a deephigh-concentration n-type impurity diffusion region 10 are formed foreach of the source region and drain region in this way, the source anddrain regions have a lightly doped drain (LDD) structure, therebypreventing electric field concentration under an end of the gateelectrode 6 a. The cobalt silicide film 12 is formed over the surface ofthe deep high-concentration n-type impurity diffusion region 10. Thecobalt silicide film 12 is formed in order to decrease the resistance ofthe source and drain regions.

Next, the p-channel MISFET is described. The p-channel MISFET has a gateinsulation film 4 over the n-type well 3 b and a gate electrode 6 b isformed over the gate insulation film 4. The gate electrode 6 b is alaminate comprised of a polysilicon film 5 and a cobalt silicide film 12formed over the polysilicon film 5. The cobalt silicide film 12 isformed in order to decrease the resistance of the gate electrode 6 b.

Side walls 9 are formed on both sides of the gate electrode 6 b and ashallow low-concentration p-type impurity diffusion region 8 is formedin the semiconductor substrate 1S just beneath each side wall 9. Thisshallow low-concentration p-type impurity diffusion region 8 is asemiconductor region in which p-type impurities such as boron areintroduced in the semiconductor substrate 1S and it is formed in a wayto match the gate electrode 6 b. In the semiconductor substrate 1S, adeep high-concentration p-type impurity diffusion region 11 is formedoutside the shallow low-concentration p-type impurity diffusion region8. This deep high-concentration p-type impurity diffusion region 11 isalso a semiconductor region in which p-type impurities such as boron areintroduced in the semiconductor substrate 1S and it is formed in a wayto match the side wall 9.

The shallow low-concentration p-type impurity diffusion region 8 anddeep high-concentration p-type impurity diffusion region 11 form asource region and a drain region for a p-channel MISFET. When a shallowlow-concentration p-type impurity diffusion region 8 and a deephigh-concentration p-type impurity diffusion region 11 are formed foreach of the source region and drain region in this way, the source anddrain regions have a lightly doped drain (LDD) structure, therebypreventing electric field concentration under an end of the gateelectrode 6 b. The cobalt silicide film 12 is formed over the surface ofthe deep high-concentration p-type impurity diffusion region 11. Thecobalt silicide film 12 is formed in order to decrease the resistance ofthe source and drain regions.

Next, a wiring structure for coupling with the CMISFET will bedescribed. An interlayer insulation film 13 (silicon oxide film) isformed over the CMISFET so as to cover the CMISFET. A contact hole 14 ismade in the interlayer insulation film 13 so as to penetrate theinterlayer insulation film 13 and reach the cobalt silicide film 12 inwhich the source and drain regions are formed. Inside the contact hole14, a titanium/titanium nitride film 15 a as a barrier conductive filmis formed and a tungsten film 15 b is buried in the contact hole 14. Aconductive plug 16 is produced by burying the titanium/titanium nitridefilm 15 a and tungsten film 15 b in the contact hole 14 in this way.Wiring 18 is formed over the interlayer insulation film 13 and thiswiring 18 and the plug 16 are electrically coupled. The wiring 18 is,for example, a laminate comprised of a titanium/titanium nitride film 17a, an aluminum film 17 b and a titanium/titanium nitride film 17 c. Aninterlayer insulation film 19 is formed over the wiring 18.

Furthermore, a multilayer wiring layer is formed over the interlayerinsulation film 19 and the above-mentioned top wiring layer is formed atits top. What is formed over the top wiring layer is shown in FIGS. 5and 6. The semiconductor device (LCD driver) in this embodiment isstructured as described above.

Next, how the CMISFET thus structured in this embodiment operates willbe briefly explained. The n-channel MISFET is taken as an example toexplain operation of the CMISFET. First, how the n-channel MISFET isturned ON is explained. As a prescribed voltage above a threshold isapplied to the gate electrode 6 a, a channel as an n-type semiconductorregion is formed in the surface of the semiconductor substrate 1S(p-type well 3 a) just beneath the gate electrode 6 a. Here, since thesource region and drain region are n-type semiconductor regions, thesource region and drain region are electrically coupled through thechannel. Therefore, when a difference in potential between the sourceand drain regions is given, an electric current flows between the sourceand drain regions. This turns ON the n-channel MISFET.

Next, how the n-channel MISFET is turned OFF is explained. As aprescribed voltage below the threshold is applied to the gate electrode6 a, the channel formed in the surface of the semiconductor substrate 1S(p-type well 3 a) beneath the gate electrode 6 a disappears. As thechannel disappears, the source region and drain region which have beenelectrically coupled through the channel are electrically isolated formeach other. Therefore, an electric current ceases to flow between thesource and drain regions. This turns OFF the n-channel MISFET. Byturning ON and OFF the n-channel MISFET in this way, the integratedcircuit of the LCD driver operates in a prescribed manner.

Next, a method of manufacturing a semiconductor device (LCD driver)according to this embodiment will be described referring to drawings.FIG. 21 is a flowchart showing the sequence of manufacturing a CMISFET.First, the process of forming a CMISFET and a first wiring layer will bedescribed referring to FIGS. 20 and 21.

First of all, a silicon monocrystal semiconductor substrate 1S dopedwith p-type impurities such as boron (B) is prepared. At this moment,the semiconductor substrate 1S is a virtually disc-shaped semiconductorwafer. Then, element isolation regions 2 are formed in the CMISFETformation region of the semiconductor substrate 1S (S101). The elementisolation regions 2 are intended to prevent elements from interferingwith each other. The element isolation regions 2 can be formed, forexample, using the LOCOS (local oxidation of silicon) or STI (shallowtrench isolation) method. In the case of using the STI method, anelement isolation region 2 is formed as follows. An element isolationtrench is made by photolithography and etching. Then, a silicon oxidefilm is formed over the semiconductor substrate 1S so as to fill theelement isolation trench and unwanted silicon oxide film over thesemiconductor substrate 1S is removed by chemical mechanical polishing(CMP). Thus an element isolation region 2 with silicon oxide film buriedonly in the element isolation trench is created.

Next, wells are formed by introducing impurities in active regionsisolated by element isolation regions (S102). For instance, a p-typewell 3 a is formed in an n-channel MISFET formation region as an activeregion and an n-type well 3 b is formed in a p-channel MISFET formationregion as an active region. The p-type well 3 a is formed by introducingp-type impurities such as boron by ion implantation. Similarly then-type well 3 b is formed by introducing n-type impurities such asphosphor (P) or arsenic (As) by ion implantation.

Next, semiconductor regions for channels (not shown) are formed over thesurfaces of the p-type well and n-type well. The semiconductor regionsfor channels are intended to control the threshold for channelformation.

Next, a gate insulation film 4 is formed over the semiconductorsubstrate 1S (S103). The gate insulation film 4 is, for example, asilicon oxide film which can be made by thermal oxidation or a similartechnique. The material of the gate insulation film 4 is not limited tosilicon oxide but may be one among other various materials such assilicon oxynitride (SiON). It may be nitride precipitation in theinterface between the gate insulation film 4 and semiconductor substrate1S. The silicon oxynitride film is more effective in decreasing theinterface state density and reducing electron traps than the siliconoxide film. Therefore, it increases the hot carrier reliability of thegate insulation film 4 and enhances the dielectric strength. Inaddition, the silicon oxynitride film is less easy for impurities topenetrate than the silicon oxide film. Hence, the use of siliconoxynitride film for the gate insulation film 4 minimizes thresholdvoltage fluctuations caused by diffusion of impurities in the gateelectrode into the semiconductor substrate. The silicon oxynitride filmcan be formed, for example, by heat treatment of the semiconductorsubstrate 1S in a nitrogen gas atmosphere containing NO, NO₂ or NH₃. Asimilar effect can be achieved by forming a gate insulation film 4 ofsilicon oxide over the surface of the semiconductor substrate 1S, andthen thermally treating the semiconductor substrate 1S in a nitrogen gasatmosphere to induce nitrogen precipitation in the interface between thegate insulation film 4 and semiconductor substrate 1S.

Alternatively, the gate insulation film 4 may be a high dielectricconstant film which has a higher dielectric constant than the siliconoxide film. In the past, the silicon oxide film has been used for thegate insulation film 4 for the reason that it provides high dielectricstrength and the interface between silicon and silicon oxide iselectrically and physically stable. However, with the growing tendencytoward microscopic devices, a very thin gate insulation film 4 is indemand. If a very thin silicon oxide film is used for the gateinsulation film 4, a so-called tunnel current may be generated whereelectrons flowing in a MISFET channel flow to the gate electrode througha barrier formed by the silicon oxide film.

For this reason, there is a growing tendency to use a material with ahigher dielectric constant than silicon oxide which can be thicker whileit provides the same capacitance. Since a high dielectric constant filmcan provide the same capacitance even when it is thicker, leak currentscan be reduced.

For instance, a hafnium oxide (HfO₂) film is used as a high dielectricconstant film in this case. Instead of hafnium oxide films, otherhafnium films such as hafnium aluminate film, HfON film (hafniumoxynitride film), HfSiO film (hafnium silicate film), HfSiON film(hafnium silicon oxynitride film) and HfAlO film may be used.Furthermore, these hafnium insulation materials may be combined withother various oxides such as tantalum oxide, niobium oxide, titaniumoxide, zirconium oxide, lanthanum oxide, and yttrium oxide to preparehafnium insulation films. Since these hafnium insulation films provide ahigher dielectric constant than silicon oxide films like hafnium oxidefilms and silicon oxynitride films, they achieve the same effects aswhen hafnium oxide films are used.

Next, a polysilicon film 5 is formed over the gate insulation film 4.The polysilicon film 5 can be formed by CVD or a similar technique.Then, n-type impurities such as phosphor or arsenic are introduced intothe polysilicon film 5 formed in the n-channel MISFET formation regionby photolithography and ion implantation. Similarly, p-type impuritiessuch as boron are introduced into the polysilicon film 5 formed in thep-channel MISFET formation region.

Next, the polysilicon film 5 is etched using the patterned resist filmas a mask to form a gate electrode 6 a in the n-channel MISFET formationregion and form a gate electrode 6 b in the p-channel MISFET formationregion (S104).

Here, n-type impurities are introduced into the polysilicon film 5 ofthe gate electrode 6 a in the n-channel MISFET formation region. Hence,the work function value of the gate electrode 6 a can be a value nearsilicon's conduction band (4.15 eV) and the threshold voltage for then-channel MISFET can be decreased. On the other hand, p-type impuritiesare introduced into the polysilicon film 5 of the gate electrode 6 b inthe p-channel MISFET formation region. Hence, the work function value ofthe gate electrode 6 b can be a value near silicon's valence band (5.15eV) and the threshold voltage for the p-channel MISFET can be decreased.In this way, in this embodiment 1, the threshold voltages for both then-channel MISFET and p-channel MISFET can be decreased (dual gatestructure).

Next, a shallow low-concentration n-type impurity diffusion region 7which matches the gate electrode 6 a of the n-channel MISFET is formedby photolithography and ion implantation. The shallow low-concentrationn-type impurity diffusion region 7 is a semiconductor region. Similarlya shallow low-concentration p-type impurity diffusion region 8 is formedin the p-channel MISFET formation region. The shallow low-concentrationp-type impurity diffusion region 8 is formed so as to match the gateelectrode 6 b of the p-channel MISFET. The shallow low-concentrationp-type impurity diffusion region 8 can be formed by photolithography andion implantation (S105).

Next, a silicon oxide film is formed over the semiconductor substrate1S. The silicon oxide film can be formed by CVD or a similar technique.By anisotropic etching of the silicon oxide film, side walls 9 areformed as side walls of the gate electrodes 6 a and 6 b (S106). Althougha single layer film of silicon oxide is used to form the side walls 9,the side walls 9 are not limited thereto and a laminate comprised ofsilicon nitride and silicon oxide films may also be used for the sidewalls.

Then, a deep high-concentration n-type impurity diffusion region 10which matches the side walls 9 is formed in the n-channel MISFETformation region by photolithography and ion implantation (S107). Thedeep high-concentration n-type impurity diffusion region 10 is asemiconductor region. The deep high-concentration n-type impuritydiffusion region 10 and the shallow low-concentration n-type impuritydiffusion region 7 configure a source region. Similarly the deephigh-concentration n-type impurity diffusion region 10 and the shallowlow-concentration n-type impurity diffusion region 7 configure a drainregion. When the source region and drain region are each comprised of ashallow n-type impurity diffusion region and a deep n-type impuritydiffusion region in this way, the source and drain regions have a LDD(Lightly Doped Drain) structure.

Similarly a deep high-concentration p-type impurity diffusion region 11which matches the side walls 9 is formed in the p-channel MISFETformation region. The deep high-concentration p-type impurity diffusionregion 11 and the shallow low-concentration p-type impurity diffusionregion 8 configure a source region and a drain region. Therefore, in thep-channel MISFET as well, the source and drain regions have an LDDstructure.

After deep high-concentration n-type impurity diffusion regions 10 anddeep high-concentration p-type impurity diffusion regions 11 are thusformed, heat treatment is made at 1000° C. or so to activate theintroduced impurities.

After that, a cobalt film is formed over the semiconductor substrate ina way that it directly contacts the gate electrodes 6 a and 6 b.Likewise, the cobalt film directly contacts the deep high-concentrationn-type impurity diffusion regions 10 and deep high-concentration p-typeimpurity diffusion regions 11.

The cobalt film can be made by sputtering or a similar technique. Byheat treatment after formation of the cobalt film, reaction between thepolysilicon film 5 of the gate electrode 6 a (6 b) and the cobalt filmis induced to form a cobalt silicide film 12 (S108). Consequently thegate electrode 6 a (6 b) becomes a laminate comprised of the polysiliconfilm 5 and cobalt silicide film 12. The cobalt silicide film 12 isintended to decrease the resistance of the gate electrode. Likewise,heat treatment as mentioned above induces reaction between the siliconand the cobalt film in the surface of each of the deephigh-concentration n-type impurity diffusion regions 10 and deephigh-concentration p-type impurity diffusion regions 11 to form a cobaltsilicide film 12. Therefore, the resistance is also decreased in thedeep high-concentration n-type impurity diffusion regions 10 and deephigh-concentration p-type impurity diffusion regions 11.

The unreacted cobalt is removed from the semiconductor substrate 1S. Itis also possible to form a nickel silicide film or titanium silicidefilm instead of the cobalt silicide film 12 in this embodiment 1.

Next, a silicon oxide film for an interlayer insulation film 13 isformed over the main surface of the semiconductor substrate 1S (S109).This silicon oxide film can be formed by CVD (chemical vapordeposition), using, for example, TEOS (Tetra Ethyl Ortho Silicate) asits material. Then, the surface of the silicon oxide film is flattenedby CMP or a similar technique.

Next, a contact hole 14 is made in the silicon oxide film byphotolithography and etching. Then, a titanium/titanium nitride film 15a is formed on the silicon oxide film of the contact hole 14 includingits bottom and inner wall. The titanium/titanium nitride film 15 a is alaminate comprised of a titanium film and a titanium nitride film andcan be formed by sputtering or a similar technique. Thetitanium/titanium nitride film 15 a functions as a barrier to preventthe tungsten, the material for the film to be buried at a next step,from diffusing into the silicon.

Next, a tungsten film 15 b is formed all over the main surface of thesemiconductor substrate 1S in a way to fill the contact hole 14. Thistungsten film 15 b can be formed by CVD or a similar technique. A plug16 is formed by removing unwanted parts of the titanium/titanium nitridefilm 15 a and tungsten film 15 b over the silicon oxide film by CMP or asimilar technique (S110).

Next, a titanium/titanium nitride film 17 a, an aluminum film 17 bcontaining copper, and a titanium/titanium nitride film 17 c are formedover the silicon oxide film and plug 16 successively. These films can beformed by sputtering or a similar technique. Then, these films arepatterned by photolithography and etching to form wiring 18 (S111).Furthermore, wiring is formed over the wiring to form a multilayerwiring. The multilayer wiring is formed over the semiconductor substrate1S in this way.

Next, steps which follow the process of forming the top wiring layer ofthe multilayer wiring layer will be described referring to drawings. Asillustrated in FIG. 22, first, an interlayer insulation film is formed.The interlayer insulation film is a laminate comprised of a siliconoxide film 20 and a silicon oxide film 21. The silicon oxide film 20 canbe formed by plasma CVD (Chemical Vapor Deposition) or a similartechnique. For the silicon oxide film 21, TEOS is used as the material.

Next, a conductive film 22 is formed over the silicon oxide film 21. Theconductive film is, for example, an aluminum film which can be formed bysputtering or a similar technique. Actually in the conductive film 22,the aluminum film is sandwiched between an upper titanium/titaniumnitride film and a lower one. As illustrated in FIG. 23, the conductivefilm 22 is processed by photolithography and etching. By processing theconductive film 22, a top wiring layer is formed over the silicon oxidefilm 21. For example, the top wiring layer includes pads PD, wirings L1,and dummy patterns DP. Dummy patterns DP are formed in the space betweenwirings L1. The dummy patterns DP, which lie in the same layer as thewirings L1, reduce the level difference between the wirings L1 andspace.

Next, as shown in FIG. 24, a silicon oxide film 22 a which covers thetop wiring layer is formed. The silicon oxide film 22 a can be formed byplasma CVD or a similar technique. The dummy patterns DP, which areformed in the top wiring layer so as to fill the space between wiringsL1, reduce irregularities which reflect the irregular surface of thesilicon oxide film 22 a. In other words, since the dummy patterns DPfill the space between wirings L1, surface irregularities of the siliconoxide film 22 a are reduced.

Then, as illustrated in FIG. 25, a silicon oxide film 23 is formed overthe silicon oxide film 22 a. For example, the silicon oxide film 23 canbe formed using TEOS as its material by CVD. Then, as illustrated inFIG. 26, the surface of the silicon oxide film 23 is flattened by CMP(chemical mechanical polishing) or a similar technique. CMP is apolishing technique in which the semiconductor substrate surface ispressed against an abrasive pad while an abrasive liquid (slurry)containing silica particles flows on the semiconductor substrate. Thetechnique uses both a chemical mechanism to oxide the surface of thematerial to be polished with a slurry and a mechanical mechanism to chipoff the oxidized layer mechanically.

The silicon oxide film 22 a which underlies the silicon oxide film 23has a less irregular surface thanks to the dummy patterns DP. Therefore,the silicon oxide film 23 formed over the silicon oxide film 22 a alsohas a less irregular surface. The process of polishing the silicon oxidefilm 23 (by CMP) to flatten its surface is relatively easy because thesilicon oxide film 23 has a less irregular surface. Namely, formation ofdummy patterns DP in the top wiring layer makes it easy to flatten thesilicon oxide film 23 at a later step.

Next, as illustrated in FIG. 27, a silicon nitride film 24 is formedover the silicon oxide film 23. The silicon nitride film 24 can beformed by plasma CVD or a similar technique. A surface protection filmcomprised of the silicon oxide film 22 a, silicon oxide film 23 andsilicon nitride film 24 is thus formed over the top wiring layer.

Next, as illustrated in FIG. 28, an opening 25 is made in the surfaceprotection film by photolithography and etching. This opening 25 isformed over a pad PD to expose the pad PD surface. The size of theopening is smaller than that of the pad PD.

Next, as illustrated in FIG. 29, a UBM film (Under Bump Metal) film 26is formed over the surface protection film including the inside of theopening 25. The UBM film 26 can be formed by sputtering or a similartechnique. The UBM film 26 is a single layer film or laminated filmincluding a titanium film, nickel film, palladium film,titanium-tungsten alloy film, titanium nitride film and/or gold film.The UBM film 26 has not only the function to improve adhesion of bumpelectrodes to pads and the surface protection film but also the barrierfunction to suppress or prevent movement of metal elements of the goldfilm formed at a later step to wirings L1, etc. or movement of metalelements of wirings L1, etc. to the gold film.

Next, as illustrated in FIG. 30, after a resist film 27 is coated on theUBM film 26, patterning is done on the resist film 27 by light exposureand development. Patterning must be done so as not to leave the resistfilm 27 in bump electrode formation regions. Then, as illustrated inFIG. 31, a gold film 28 is formed by plating. The gold film 28 lies overthe surface protection film (silicon nitride film 24) and is also buriedin the opening 25. When the gold film 28 is buried in the opening 25, aplug SIL is completed.

Then, as illustrated in FIG. 32, a bump electrode BP1, comprised of thegold film 28 and UBM film 26, is formed by removing the patterned resistfilm 27 and the UBM film 26 covered by the resist film 27. The bumpelectrode BP1 is larger than the pad PD and wirings L1 lie in the topwiring layer beneath the bump electrode BP1. The presence of wirings L1beneath the bump electrode BP1 permits effective use of the spacebeneath the bump electrode, leading to a smaller semiconductor device.In addition, when dummy patterns DP lie beneath the bump electrode BP1in addition to wirings L1 as power lines or signal lines, the flatnessof the surface protection film formed over the top wiring layer isincreased. In other words, if only power lines and signal lines (wiringsL1) are formed in the top layer of the multilayer wiring layer, surfaceirregularities caused by the power lines and signal lines (wirings L1)would be serious because the top wiring layer cannot be densely filledwith wirings. By forming dummy patterns DP as well as wirings in thelayer, the flatness of the top wiring layer is increased. Furthermore,since the surface of the surface protection film is flattened by CMP,the flatness of the surface protection film formed over the top wiringlayer is guaranteed and the flatness of bump electrodes formed over thesurface protection film is increased. After that, individualsemiconductor chips are obtained by dicing the semiconductor substrate.

Next, a semiconductor chip obtained by the above process is mounted on amounting substrate by bonding. FIG. 33 shows that a semiconductor chipCHP is mounted on a glass substrate 30 (COG: Chip On Glass). Asillustrated in FIG. 33, a glass substrate 31 is mounted on the glasssubstrate 30, thereby forming an LCD screen. The semiconductor chip CHP,an LCD driver, is mounted on the glass substrate 30 near the LCD screen.Bump electrodes BP1 and BP2 are formed in the semiconductor chip CHP andthe bump electrodes BP1 and BP2 are coupled with terminals formed overthe glass substrate 30 through ACF (Anisotropic Conductive Film). Theglass substrate 30 and a flexible printed circuit board 32 are alsocoupled through ACF. In the semiconductor chip CHP mounted on the glasssubstrate 30, the bump electrode BP2 for output signals is electricallycoupled with the LCD screen and the bump electrode BP1 for input signalsis coupled with the flexible printed circuit board 32.

FIG. 34 shows the semiconductor chip CHP mounted on the glass substrate30 in an enlarged form. As illustrated in FIG. 34, terminals 30 a areformed over the glass substrate 30 and these terminals 30 a areelectrically coupled with the bump electrodes BP1 and BP2. The bumpelectrodes BP1 and BP2 and the terminals 30 a are not in direct contactwith each other but coupled through ACF. The ACF is a film made bymixing conductive fine metal particles 33 with thermosetting resin andshaping the mixture into a membrane. Each of the metal particles 33 is aspherical body with a diameter of 3-5 μm which is comprised of a nickellayer and a gold coating layer as its inner layers and an insulationlayer as its outmost layer.

When the semiconductor chip is mounted on the glass substrate 30, theACF is placed between the terminals 30 a of the glass substrate 30 andthe bump electrodes BP1 and BP2 of the semiconductor chip CHP. As thesemiconductor chip CHP is pressurized by applying heat by a heater orthe like, pressure is applied only to areas where the bump electrodesBP1 and BP2 lie. This causes metal particles 33 dispersed in the ACF tocontact and overlap each other and be pushed against each other. As aconsequence, a conductive path is made in the ACF through metalparticles 33. Since metal particles of the ACF to which pressure has notbeen applied hold their surface insulation layers, insulation betweenneighboring bump electrodes BP1 and between neighboring bump electrodesBP2 is retained. This offers an advantage that even when the intervalbetween bump electrodes BP1 or BP2 is narrow, the semiconductor chip CHPis mounted on the glass substrate 30 without causing shorting.

In this embodiment 1, in a semiconductor chip, dummy patterns are formedin the top wiring layer and the surface protection film which covers thetop wiring layer is flattened by CMP. Therefore, the flatness of bumpelectrodes formed over the surface protection film is increased. Thisensures that the bump electrodes contact metal particles in ananisotropic conductive film properly throughout the bump electrodes.This improves the reliability in coupling between the bump electrodes ofthe semiconductor chip and terminals (wirings)) of the mountingsubstrate.

FIG. 35 shows the general structure of an LCD (liquid crystal displaydevice 35). As illustrated in FIG. 35, an LCD screen 34 is formed on aglass substrate where images appear on this screen 34. A semiconductorchip CHP as an LCD driver is mounted on the glass substrate near thescreen 34. A flexible printed circuit board 32 is mounted near thesemiconductor chip CHP and the semiconductor chip as a driver is placedbetween the flexible printed circuit board 32 and LCD screen 34. Thesemiconductor chip CHP is thus mounted on the glass substrate. Thesemiconductor chip CHP as an LCD driver is thus mounted on the liquidcrystal display device 35.

The invention made by the present inventors has been so far concretelydescribed in reference to preferred embodiments thereof. However, thepresent invention is not limited to the embodiments and it is obviousthat the invention may be modified in various ways without departingfrom the spirit and scope thereof.

The invention can be widely used in the semiconductor devicemanufacturing industry.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate having a first side extending along a firstdirection, a second side extending along the first direction and beingopposite to the first side, a third side extending along a seconddirection perpendicular to the first direction, and a fourth sideextending along the second direction and being opposite to the thirdside; a multilayer wiring structure formed over the semiconductorsubstrate; a first pad electrode, a second pad electrode and dummypatterns formed in an uppermost layer of the multilayer wiringstructure; a first insulating film formed over the first pad electrode,the second pad electrode and the dummy patterns; a first opening and asecond opening formed in the first insulating film and located over thefirst pad electrode and the second pad electrode, respectively; and afirst bump electrode and a second bump electrode formed over the firstinsulating film and electrically connected to the first pad electrodeand the second pad electrode through the first opening and the secondopening, respectively, wherein the first pad electrode and the secondpad electrode are located near the first side, at substantially a samedistance from the first side, and are spaced along the first directionin a plan view, and wherein, in the first direction, at least one of thedummy patterns is located between the first pad electrode and the secondpad electrode in the plan view.
 2. A semiconductor device according tothe claim 1, wherein some of the dummy patterns are located under thefirst bump electrode.
 3. A semiconductor device according to the claim2, wherein the first insulating film includes a silicon oxide film and asilicon nitride film formed over the silicon oxide film.
 4. Asemiconductor device according to the claim 3, wherein a top surface ofthe silicon oxide film is flattened by a polishing treatment.
 5. Asemiconductor device according to the claim 1, wherein the firstinsulating film includes a silicon oxide film and a silicon nitride filmformed over the silicon oxide film.
 6. A semiconductor device accordingto the claim 5, wherein a top surface of the silicon oxide film isflattened by a polishing treatment.
 7. A semiconductor device accordingto the claim 1, wherein a length of the first side is larger than alength of the third side.
 8. A semiconductor device according to theclaim 7, wherein the semiconductor device is an LCD driver for a liquidcrystal display.
 9. A semiconductor device according to the claim 8,wherein the first bump electrode and the second bump electrode includeAu.